The present invention relates to a rotational phase difference adjusting means which is arranged between two rotational shafts to adjust a rotational phase difference therebetween, and which may be used in an internal combustion engine to change an action phase of each of an intake valve and an exhaust valve according to a condition of the internal combustion engine.
In a conventional valve action phase difference adjusting device disclosed by Publication of Japanese Patent Unexamined Publication No. 2-241914, as shown in FIG. 4, a timing pulley 16 which is driven by a crank shaft of an internal combustion engine through a timing belt is supported on a cam shaft 12 in a rotatable manner through a cylindrical sleeve 16c extending from the timing pulley 16. A cylindrical ring gear 22 is arranged between the cylindrical sleeve 16c and a damper case 15 which is fixed to the cam shaft 12 to rotate together therewith. The ring gear 22 has helical splines on an inner cylindrical surface and outer cylindrical surface thereof, and the helical splines with respective helical angles relative to an axis of the cam shaft 12 engage with helical splines on an inner surface of the damper case 15 and on an outer surface of the cylindrical sleeve 16c, respectively. A torque applied to the pulley 16 is transmitted from the cylindrical sleeve 16c to the damper case 15 through the ring gear 22 to drive the ring gear 22. When the ring gear 22 is moved in an axial direction of the cam shaft 12 by a hydraulic force, a relative rotation between the damper case 15 and the cylindrical sleeve 16c is generated along the helical splines so that a rotational phase difference between the cam shaft 12 and the pulley 16 is adjusted. The damper case 15 has a combination of a disk portion extending radially and a plurality of tube-shaped projections therefrom on an outer periphery thereof. A viscous damper 17 is formed between the tube-shaped projections and a plurality of labyrinth grooves receiving the tube-shaped projections in the pulley 16. A viscous fluid of the viscous damper 17 is received in a sealing manner by a space formed by the pulley 16, the damper case 15 and a cover 18 fixed to the pulley 16. A shearing force generated between the tube-shaped projections and the labyrinth grooves according to the relative rotation between the damper case 15 and the pulley 16 decelerates or absorbs a vibration of the ring gear 22 and/or the cam shaft 12. Oil-seats 19 and 21 prevent the viscous fluid from flowing oil from the space among the pulley 16, the damper case 15 and the cover 18.